LED projectors have been proposed in which light-emitting diodes (LEDs) are used as the light-emitting devices included in the light source apparatuses. This type of LED projector is configured equipped with a light source apparatus having LEDs, an illumination optical system into which light emitted from the light source apparatus is irradiated, a light valve having a liquid crystal display panel into which light from the illumination optical system is irradiated, and a projection optical system for projecting light from the light valve onto a projection surface.
In order to increase the luminance of an image that is projected by an LED projector, all possible measures need to be taken to eliminate light loss in the optical path from the light source apparatus to the light valve.
In addition, as disclosed in Non-Patent Document 1 discloses limitations caused by etendue, which is determined by the product of the surface area of the light source apparatus and the angle of radiation. In other words, light from the light source apparatus is not utilized as projection light if the value of the product of the angle of radiation and the surface area of light emission of the light source apparatus is not made equal to or lower than the value of the product of the surface area of the incident surface of the light valve and the acceptance angle (solid angle) that is determined by the f-number of the projection lens.
As a result, in a light source apparatus that has LEDs and an optical element into which light from the LEDs is irradiated, realizing a reduction of the above-described light loss by decreasing the etendue of light emitted from the optical element remains an unresolved problem.
In a light source apparatus that is equipped in an LED projector, it is absolutely imperative that a plurality of LEDs be employed to compensate for the insufficient amount of light generated by a single LED of a single LED and thus realize projected luminous flux on the order of several thousand lumens.
As one example of a light source apparatus that uses a plurality of LEDs in this way, Patent Document 1 discloses a light source unit, as shown in FIG. 1, that is equipped with: a plurality of monochromatic light source apparatuses 83a-83f having LEDs 84a-84f, optical axis alignment parts 82a-82d that cause the optical axes of light emitted from these monochromatic light source apparatuses 83a-83f to coincide, light source sets 81a and 81b into which light from these optical axis alignment parts 82a-82d is irradiated, and light guide apparatus 80 into which light from these light source sets 81a and 81b is irradiated. In this light source unit, light from the plurality of monochromatic light source apparatuses 83a-83f is synthesized, and light for which the angle of radiation has been constricted by light source sets 81a and 81b is irradiated into light guide apparatus 80. In this configuration, a reduction of light loss is achieved by light source sets 81a and 81b that constrict the angle of radiation of light that is irradiated into light guide apparatus 80.
Alternatively, as another example of a light source apparatus that uses a plurality of LEDs, Patent Document 2 discloses a light source apparatus as shown in FIG. 2 that is equipped with light source substrate 86 on which a plurality of LEDs 85 are arranged on a plane. This light source apparatus is provided with an optical element composed of two prism sheets 88 and 89 that each have prism rows formed on one surface and that are each arranged such that the prism rows of one sheet are orthogonal to the prism rows of the other, and frame 87 that supports these prism sheets 88 and 89. In this light source apparatus, light from the plurality of LEDs 85 is synthesized by the two prism sheets 88 and 89.